Simultaneous Determination of the Time and Space Correlations of Density Fluctuation in Glass Transition of Supercooled Liquid

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The purpose of this study is to investigate the possibility of the time-space sealing law associated with glass transition of supercooled liquid. The impulsive stimulated thermal scattering (ISTS : one of time-domain measurements) has been performed for this purpose. ISTS can determine not only the time correlation of the density fluctuation directly but also the space correlation of the density fluctuation at the same time by changing the scattering wave vector q (changing the observation length scale Λ = 2π/q).The density fluctuation has been observed in three typical glass forming liquids ; D-sorbitol, glycerol, and salol. The q dependence of the density fluctuation has been successfully measured and the new phenomenon has been found commonly in these materials. The relaxation time τ_R of the density fluctuation shows an anomalous peak at the particular temperature T_<max> (much higher than the glass transition temperature T_g). Moreover, we firstly found that T_<max> approaches T_g with decreasing in q. This phenomenon implies the existence of the length scale ξ characterizing the space correlation of the density fluctuation. Since it is natural to think that ξ is growing with decreasing in temperature, we think that T_<max> is the temperature where ξ = Λ.